Electric switch with contact protector



F. A. DENES ETAL ELECTRIC SWITCH WITH CONTACT PROTECTOR July 30, 1968 2Sheets-Sheet 1 Filed Feb. 17, 1966 S T Z MUSJ EDE D M L A E R N ENE! UmmP J EW Y. B

July 30. 1968 P. A. DENES ETAL ELECTRIC SWITCH WITH CONTACT PROTECTOR 2Sheets-Sheet 2 Filed Feb. 17, 1966 //VV7VTOR$ PETER A. DENES JOHN L.HAYDU EUGENE S. LESZT United States Patent 3,395,316 ELECTRIC SWITCHWITH CONTACT PROTECTOR Peter A. Denes, Albuquerque, N. Mex., John L.Haydn,

Milwaukee, Wis., and Eugene S. Leszt, Alhambra,

Calif., assignors to Allen-Bradley Company, Milwaukee, Wis., acorporation of Wisconsin Filed Feb. 17, 1966, Ser. No. 528,288 2 Claims.(Cl. 31711) ABSTRACT OF THE DISCLOSURE Contact protecting means for anAC. electrical switch including double break contacts to form at leasttwo air gaps in series. At least one unidirectional current conductingdevice arranged to shunt the opened controls in parallel with one gapand providing a low impedance path for one-half cycle of an AC. currentsource and a high impedance path during the other one-half cycle.

The present invention relates to a combination of an alternating currentswitch with contact protecting means designed to close and open anelectrical circuit path between an electrical source and an electricalload and to limit arcing between open switch contacts to a specifiedtime. More specifically, the invention pertains to a switching meanswhich when fully open establishes at least a double break with the pathto form at least two air gaps in series and protecting means including aunidirectional current conducting device extending between the openedcontacts in parallel with one gap and which unidirectional currentconducting device provides a path shunting the associated gap, said pathbeing of low impedance for one-half cycle of the alternating currentsource and of high impedance during the other one-half cycle.

Any given size alternating current electrical switch can switch offwithin a given time period, e.g. a half cycle only of a limited currentvalue. The limit of the current is determined by the switchconstruction. Current values above the limit maintain an arc whichfrequently exists for a time duration of several half cycles. Such along duration of an arc tends to deteriorate the contacts and frequentlyleads to complete switch destruction. Thus, it is desirable tosubstantially eliminate arcing or limit it to the shortest timepossible-preferably to one or two half cycles. To extinguish the arc,prior art devices frequently utilize complex, space consuming arc chutesand other are squelching arrangements. In some devices the contacts areopened a wide distance to distinguish the arc. However, this requires alarge mechanical structure which consumes space and demands largeamounts of energy for operation plus a sturdy mechanical structure towithstand the impact of the closing contacts.

The present invention provides a switch and unidirectional conductingdevice in combination in which arcing across a given pair of contacts issubstantially eliminated or limited to a short time period. Depending onthe embodiment, the arc may be eliminated within one or two one-haltcycles of the power source. Advantages of this invention include ashorter distance between the opened contacts which aids longer contactwear and a smaller electromagnet for opening and closing the contactswhen used in connection with an electromagnetic contactor. Thus, for agiven application, the switch can be miniaturized and simplified overdesigns heretofore available.

In general, the present invention pertains to an electrical switchingmeans designed to provide double break contacts with a center tapbetween the breaks. The double break arrangement provides a pair of airgaps in series upon operating the switching means to an open position.

To realize the double break, the switching means may include a pair ofsingle break switches connected in series or a contactor having doublebreak contacts actuated by an electromagnet. Such electromagneticcontactors are commonly used for repeatedly establishing andinterrupting an electric power circuit. Shunting one or both air gaps ofthe switching means is a unidirectional con ducting device. The devicemay be in the form of a power rectifier, such as a silicon or germaniumdiode. For example, if a diode is placed across each gap with thepolarities of the diodes being opposite to one another, each diodealternatively provides a low impedance path around its associated gap onalternate half cycles of the power source. When the switch is operatedto open the circuit, one gap is flanked by a low impedance path so thatthe associated contacts can initially open without current flowingtherethrough, and thus without arcing or ionizing the gap. Concurrently,due to the high impedance flanking the second air gap, an arc may beformed across that gap causing it to be ionized. However, during thenext one-half cycle, the previously ionized gap has a low impedance patharound it though the associated unidirectional contacting device is nowblocking the current, as is the associated gap which was notpro-ionized. Thus, the current will not flow during the second one-halfcycle and arcing is substantially eliminated or limited to a one-halfcycle of the source, depending on what point of the cycle the contactsinitially open.

In the event the embodiment is designed such that only one air gap isflanked by a unidirectional path, arcing is substantially eliminated orlimited to one-half cycle or two one-half cycles depending on whetherthe undirectional conducting device is conducting or blocking when thecontacts are initially opened.

Another embodiment may include switching means designed such that theassociated gaps differ in their respective opening time by one-halfcycle. One gap is created during one-half cycle of the signal and theother gap during the next one-half cycle. In this embodiment aunidirectional conducting device across one gap will result ineliminating or limiting arcing to one-half cycle of the power source.

The foregoing features, advantages and mentioned embodiments of theinvention will further appear in the description to follow. Reference ismade in the description to the accompanying drawings which form a parthereof and in which there is shown by way of illustration and not oflimitation specific embodiments in which the invention may be practiced.

In the drawings:

FIG. 1 is a schematic wiring diagram of a pair of single break switchesdesigned to establish and interrupt an electrical circuit connecting anAC. source with a load, each of said switches being flanked by a diodein accordance with the principles of this invention.

FIG. 2 is a schematic wiring diagram similar to FIG. 1, wherein anelectromagnetic contactor with double break contacts is substituted forthe switches of FIG. 1.

FIG. 3 illustrates a modification of FIG. 2 wherein provisions areincorporated to disconnect the reverse currents of the diodes.

FIG. 4 is a schematic wiring diagram illustrating an electromagneticcontactor having two contact arrangements in which the opening time ofthe arrangements differ by one-half cycle with respect to each other,one of said contact arrangements being flanked by a diode.

FIG. 5 is a schematic wiring diagram similar to FIG. 1, in which onlyone switch is flanked by a diode.

FIGS. 1-5 illustrate various embodiments incorporating the principles ofthe present invention. In each the electrical circuit is referred to bythe general reference character 1. The various embodiments are adaptedfor connection with an A.C. power source 2 and are loaded by anelectrical load designated by a block diagram 3. Intermediate the source2 and the load 3 is an interrupter network designated by the generalreference character 4, which for illustrative purposes is surrounded bya broken-line diagram.

In FIG. 1, the interrupter network 4 includes a pair of single breakswitches 5 and 6. The switch 5 includes a stationary contact 7 and amovable contact 70, whereas the switch 6 comprises a stationary contact9 and a movable contact 9a. The contact 7 joins the source 2 at ajunction point 10. The contact 7a is connected to junction point 11 asis the contact 9 of the switch 6. The contact 9a joins a junction point12 common with one side of the load 3. The other side of the load 3 isconnected to the source 2 by means of a line connection 13. Shunting theswitch 5 is a unidirectional conducting device in the form of a diode14. The diode 14 has an anode element 15 connected to the terminal and acathode element 16 connected with the junction 11. Shunting the switch 6is a unidirectional conducting device in the form of a diode 17. Thediode 17 has an anode element 18 connected with the terminal 12 and acathode element 19 connected with the terminal 11. Though the embodimentillustrates use of a pair of unidirectional conducting devices in theform of single diodes, similar results may be realized through use of asingle, double side diode.

The embodiment of FIG. 1 is designed such that upon simultaneous openingof the contacts of the switches 5 and 6, arcing is substantiallyeliminated or limited to onehalf cycle of the A.C. source. Forexplanation of operation of the embodiment of FIG. 1, it should first beassumed that the switches S and 6 are closed to provide a continuouscircuit path between the source 2 and the load 3. Upon opening of theswitches the circuit path is interrupted. As will hereinafter becomeevident, the polarity of the power source signal when interruptioninitially occurs is immaterial. However, assuming that interruptionoccurs during the half cycle when the diode 14 is conducting, the diode14 will provide during this half cycle, a low impedance path around theswitch 5 between the terminals 10 and 11. Consequently, the current willelect the path of the diode 14 rather than attempt to cross the gapbetween the contacts 7 and 8. (Hereinafter the gap between the contacts7 and 7a will be referred to as gap 7-7a, the gap between the contacts 9and 9a as gap 9-9a, etc.) Thus, no arcing will occur across the gap7-701, and the air gap will not become ionized. At the same time, thediode 17 is blocking and offers a high impedance path around the switch6. The path across the contacts 9 and 9a otters the least impedance andaccordingly, an arc exists across the gap 9-9a. Also, as a result, thegap 9-9a will be ionized. To illustrate the current path when the diode14 conducts, it may be assumed that the lowest impedance path betweenthe source 2 and load 3 is that indicated by the broken line pathillustrated in FIG. 1.

During the next one-half cycle, the diode 17 conducts and offers a lowimpedance path. During this half cycle, the diode 14 blocks as does thegap 7-7a since the gap was not pre-ionized during the previous one-halfcycle. -In order to break down an arc over an air gap which has not beenpre-ionized, an extremely high voltage, e.g. approximately 2000 voltsper millimeter is necessary. Thus, during the second one-half cycle, thearc is substantially non-existent as the path between the source 2 andthe load 3 is open owing to the blocking of the diode 14 and thenon-preionized gap 7-7a. During the third one-half cycle, though thediode 14 could conduct, the diode 17 and the air gap 99a are insulating.During the second one-half cycle sufficient time will have elapsed forthe gap 9-9a to regain substantially its full dielectric strength. (Ithas been found that an air gap regains approximately 90% of itsdielectric strength within 7 milliseconds which is less than one-halfcycle of a standard 60 c.p.s. orSO cfpjs. source 2.) Thus, the gap 9-9ais substantially de-ionized prior to the third one-half cycle and arcingwill have been limited to the first one-half cycle.

The previous discussion has assumed the switches 5 and 6 to be initiallyopened when the diode 14 is conducting. However, the same results arerealized if the switches 5 and 6 are initially opened when the diode 17is conducting since the arrangement of the interrupter network 4 issymmetrical. In this case, the diode 17 initially provides a lowimpedance path and the diode 14 blocks. Thus, the gap 99a of the switchis substantially shorted and the gap 77a of the switch 5 may open underarcing conditions. During the next one-half cycle, the gap 7-7a isshorted by the diode 14 and the gap 9-9a blocks since it was notpre-ionized.

It may be noted that by extinguishing the are by means of the diodes,the contact movement in creating the gaps 7-7a and 9-9a may be veryshort. With the present structure, the gap is only a function of thevoltage applied to the switch, whereas in switch assemblies omitting thediodes, the gap is a function of both the voltage and current to beinterrupted. Also, the longest time that the diodes will carry thecurrent is only one-half cycle during the circuit interruption andconsequently, they can be relatively reduced in size.

The embodiments of FIG. 2 is similar to that of FIG. 1 with theexception that the two switches 5 and 6 of the interrupter network 4 arereplaced by a standard electromagnetic contactor diagrammaticallyillustrated as contained within the broken-line block diagram designatedby the general reference character 20. Elements of FIG. 2 common withthose of FIG. 1 carry the same reference numerals. The contactor 20 is adouble-break contactor having a movable contact carrier in the form of aspanner 21 carrying a pair of contacts 22 and 23 and arranged to engagea pair of stationary contacts 24 and 25, respectively. Actuation of themovable contact spanner 21 and its contacts 22 and 23 is controlled by asolenoid comprising a coil 26 encircling an armature member 27 which ismechanically connected to the contact spanner 21. Actuation of thearmature member 27 is controlled by excitation of the coil 26, whichexcitation may be supplied from an auxiliary source (not shown). Alsojoining the contact spanner 21 is a flexible electricallyconductive lead28 arranged to provide a continuous electrical connector between thespanner 21 and a junction point 29. The lead 28 flexes responsive tomovement of the armature member 27. The junction point 29 also providesa common connection between the lead 28, the diode 14 at the cathode 16and the diode 17 at the cathode 19. The anode element 15 is tied to ajunction point 10 which is electrically common to the contact 24 and oneside of the A.C. source 2. The anode element 18 is tied to the junctionpoint 12 which is electrically common to the contact 25 and one side ofthe load 3.

When the contactor 20 is in the closed state, the contact 22 engages thecontact 24 and the contact 23 engages the contact 25. In the closedstate the diodes 14, 17 and the flexible lead 28 are short circuited.When the contactor 20 is in the open state, i.e. a gap 22-24 existsbetween the contacts 22 and 24, and/or a gap 23-25 exists between thecontacts 23 and 25, one of the diodes 14 or 17, depending on theinstantaneous polarity of the source 2, is conducting and carryingcurrent. Assuming that the contacts open when the diode 14 isconducting, the gap 2224 opens without arcing and the gap 23-25 openswith consequent arcing. During the following onehalf cycle when thediode 17 conducts, the arc across the gap 23-25 is extinguished and thecurrent is interrupted. Since the gap 2224 was not pre-ionized, it hasfull dielectric strength and no arc appears across it. Likewise thediode 14 is now blocking. During the third one-half cycle, the diode 17is again blocking as is the gap 2325, since as previously mentioned inconnection with FIG. 1,

de-ionization is substantially accomplished within approximately 7milliseconds, which is less than one-half cycle for a 50 c.p.s. or 60c.p.s. power source. Again, since the arrangement of the contactor 20and diodes 14 and 17 is symmetrical, arcing is also substantiallyeliminated or limited to one-half cycle if the diode 17 is conductingwhen the switch contacts initially open.

In an open state, a small reverse current may flow through the diodes 14and 17. In many cases, this small current is tolerable. If, however,complete switching off is necessary, a further interruption may be madein series with the diodes when the main contacts are open. Such anarrangement is shown in the embodiment of FIG. 3 which is a modificationof FIG. 2. All elements common to those of FIG. 2 carry the samereference numerals in FIG. 3. In FIG. 3, the electromagnetic contactor20 carries an additional set of double break contacts interrupting theline 13 and including a pair of stationary contacts 40 and 41 and acarrier in the form of a contact spanner 42 carrying a pair of contacts43 and 44. The spanner 42 is mechanically joined to the armature 27. Thecontact relationship between the contacts 40, 41, 43 and 44 is dependenton the excitation of the coil 26 and coincides with the relationshipbetween the contacts 22, 23, 24 and 25. If the contacts 22, 23, 24 and25 are open the contacts 40, 41, 43 and 44 are likewise open. Thus,there is no continuous path for reverse current between the source 2 andthe diodes 30 and 31.

FIG. 4 illustrates another embodiment of the present invention. Itprovides interruption of the electric current within one-half cycle ortwo one-half cycles using one diode in combination with a contactorwhich has its two contacts arranged in such a way that one contact opensabout one-half cycle before the other contact. The arcing is limited toone-half cycle on each pair of contacts. In the embodiment of FIG. 4,the interrupter 4 includes an electromagnetic contactor carrying twodouble-break contact arrangements. The arrangements are designated bythe broken-line diagrams A and B. The arrangement A includes a pair ofstationary contacts 50 and 51 and a pair of movable contacts 52 and 53which are joined by a contact carrier in the form of a contact spannermember 54. The spanner 54 is mechanically joined to an armature member55. The contact arrangement B includes a pair of stationary contacts 56and 57 and a pair of movable contact spanner member 60. The spannermember 60 is mechanically connected to the armature member 55. Movementof the armature member 55 is dependent upon the excitation of a coil 61.The coil 61 may receive excitation from an auxiliary source (not shown).Shunting the contact arrangement A is the diode 14. The anode 15 ofdiode 14 is connected to the junction point 10, electrically common tothe contact 50 and one side of the source 2. The cathode 16 is connectedto a junction 66 electrically common to the contacts 51 and 56.

Assuming in the embodiment of FIG. 4 that opening of the contactarrangement B is delayed one-half cycle with respect to the opening ofthe contact arrangement A, the diode 14 will be conducting when thearrangement A initially opens, no arc occurs across the gap 50-52 or thegap 51-53 since they are shorted. The gaps 56- 58 and 57-59 do not arcas they are not open. In the next one-half cycle when the diode 14 isblocking and the contact arrangement B is open, an arc across the gaps50-52 and 51-53 is non-existent since they were not ionized during theprevious one-half cycle. Also, the gaps 56-58 and 57-59 open withoutarcing because the diode 14 is blocking as are the gaps 50-52 and 51-53since the current was interrupted within the first one-half cycle. If,on the other hand, the diode 14 is blocking when the contact arrangementA initially opens, there may be an arc across the gaps 50-52 and 51-53.However, the arc is substantially non-existent during the next one-halfcycle when the diode 14 is conducting and the contact arrangement B isopen. The contact arrangement B may open with an arc. In the thirdone-half cycle, the contact arrangement A does not re-ignite becauseduring the preceding half-time period de-ionization took place and itregained its dielectric strength. The diode 14 is blocking and hence noarcing takes place across the contact arrangement B. Consequently,arcing across the gap of any pair of contacts is substantially limitedto one-half cycle and the gap recovers by de-ionization during thesucceeding one-half cycle.

FIG. 5 is illustrative of another embodiment similar to FIG. 1 in whichthe two points of interruption may occur simultaneously, but in whichonly one gap is flanked by a unidirectional conducting device. In thisarrangement arcing is substantially eliminated within one-half cycle ortwo one-half cycles depending on whether the unidirectional conductingdevice is blocking or conducting when circuit interruption initiallyoccurs. Assuming the switches 5 and 6 open when the diode 14 isconducting, the gap 7-7a is shorted so that it opens without arcing andconsequent ionization. The gap 9-9a opens with an arc. However, duringthe next one-half cycle, the diode 14 and the gap 7-7a are bothinsulating and thereby no arcing will follow. If the diode 14 isblocking when the switches 5 and 6 initially open, arcing may berealized across the gap 7-7a and the gap 9-9a so that both gaps will bepreionized. During the next half cycle, the diode 14 shorts the gap7-7a, thereby deionizing it. But arcing may be evident across the gap9-9a since it is not yet necessarily de-ionized. However, on the thirdone-half cycle, both the diode 14 and the gap 7-7a are insulating sothat arcing is limited to two one-half cycles of the signal source.

In the foregoing, discussion has been limited to single phase switching.However, it will be obvious to those skilled in the art that theinvention can be used for multiphase switching.

In the illustrative embodiments, the switch and associatedunidirectional conducting devices may carry more electrical componentsthan presently known circuit interrupters. However, for a givenapplication, the overall device according to this invention may besmaller, more economical and more reliable. The present device permitselimination of arc extinguishing plates and chutes and other arcextinguishing devices; a shorter contact distance between openedcontacts; smaller electromagnets Where electromagnetic contactors areused; smaller arc chambers owing to the smaller arc energies; lesserosion of the contacts and longer life for a given switch.

We claim:

1. An electrical switch with contact protecting means for opening andclosing an electrical circuit relationship between an electrical sourceand an electrical load comprising, in combination:

switching means including a double break contactor providing a firstpair of contacts, a carrier carrying a second pair of contacts, andmeans for moving said carrier with respect to said first pair ofcontacts for alternatively establishing and interrupting the electricalcircuit relationship between said first and second pair of contacts,said means providing a first air gap between one contact of said firstpair of contacts and one contact of said second pair of contacts and asecond air gap between the other of said contacts of said first pair ofcontacts and the other contact of said second pair of contacts when theelectrical circuit is interrupted;

a first unidirectional electrical conducting device extending betweenand electrically shunting one of said air gaps when the circuit isinterrupted, said unidirectional device being arranged to accept currentfrom said source when the current is of one polarity and block currentflow of the opposite polarity; and

a second unidirectional electrical conducting device extending betweenand electrically shunting the other of said air gaps when the circuit isinterrupted, said second unidirectional device designed to acceptcurrent of said source when the current is of one polarity tion of saidarmature and the circuit relationship between and block current flow ofthe opposite polarity, the said first and said second pair of contacts.accepting and blocking states of the unidirectional devices beingopposite to one another such that upon References Cited interruption ofthe circuit one of said unidirectional UNITED STATES PATENTS devicesprovides a low impedance path around the associated gap while the otherof said unidirectional 2 23:

devices offers a high impedance path around its assoi dated gap3,223,888 12/ 1965 Koppelmann 31711 2. The electrical switch withcontact protecting device 10 FOREIGN PATENTS of claim 1 in which theswitching means includes an electromagnetic contactor and in which themeans for moving i came l P f armaiure and t electmmagnet MILTON o.HIRSHFIELD, Primary Examiner. sa1d armature oining said carrier and saidelectromagnet,

the excitation of said electromagnet determining the posi- 15 J. D.TRAMMELL, Assistant Examiner.

638,981 7/1932 Germany.

